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Weekly Seminars for May 2010 Print E-mail

Tuesday 11th May 2010 - 4:00 P.M.

Università "La Sapienza" Roma - Aula Careri (Physics Dept., Old Building - 1st Floor)

Speaker:  Prof. Massimo Bianchi (Dipartimento di Fisica, Università Tor Vergata - INFN, Sezione di Roma "Tor Vergata")

Title: Recent Trends in Superstring Phenomenology

Abstract: We review possible phenomenological scenari in String Theory. In particular we focus on vacuum configurations with intersecting and/or magnetized unoriented D-branes. We show how a TeV scale tension may be compatible with the existence of Large Extra Dimensions and how anomalous U(1)'s can give rise to interesting signatures at LHC or in cosmic rays.Finally, we discuss unoriented D-brane instantons as a source of non-perturbative effects that can contribute to moduli stabilization and susy breaking in combination with fluxes.


Friday 14th May 2010 - 4:00 P.M.

Università "La Sapienza" Roma - Aula Majorana (Physics Dept., Old Building - Ground Floor)

Speaker:  Prof. Paolo Salucci (SISSA, Trieste)

Title: La distribuzione di massa nelle Galassie a Spirali

Abstract: In the past years a wealth of observations has unraveled the structural properties of the Dark and Luminous mass distribution inspirals. These have pointed out to an intriguing scenario not easily explained by present theories of galaxy formation. The investigation of individual and coadded objects has shown that the spiral rotation curves follow, from their centers out to their virial radii, a Universal profile (URC) that arises from the tuned combination of a stellar disk and of a dark halo. The importance of the latter component decreases with galaxy mass. Individual objects, on the other hand, have clearly revealed that the dark halos encompassing the luminous discs have a constant density core. This resulting observational scenario poses important challenges to presently favored theoretical $\Lambda$ CDM Cosmology.


Friday 21th May 2010 - 4:00 P.M.

Università "La Sapienza" Roma - Aula Majorana (Physics Dept., Old Building - Ground Floor)

Speaker:  Dr. Alberto Benedetti (Dipartimento di Fisica Nucleare e Teorica dell'Università degli Studi di Pavia)

Title: ACCRETION ONTO PRIMORDIAL BLACK HOLES

Abstract: Primordial black holes (PBHs) are produced in the early Universe by the collapse of overdense regions. At priori they can be of any mass and, in particular, much below the stellar ones. A most striking feature of PBHs is the phenomena of Hawking radiation, which leads to their evaporation on a characteristic time scale, tev ' 101(MPBH=1015 g)3 yr, which decreases their mass. Hence, PBHs with mass MPBH < 1015 g should have already evaporated. The astrophysical and cosmological relevance of PBHs comes from the fact that they are very good candidates for the Cold Dark Matter (CDM), which is necessary to explain many observations concerning galaxies and their clusters as well the process responsible for their formation within the Big Bang cosmology. It is therefore of great importance to develop methods devoted to their observational discovery. It turns out that the leading process whereby a PBH can be identi ed is the electromagnetic radiation produced when the surrounding material falls into its gravitational eld, namely during the PBH accretion process. In this thesis we study the accretion onto PBHs; in particular we are interested in a phenomenon up to now unexplored i.e. the occurrence of the degeneracy in the accreting gas. It will be shown that during accretion the electron gas can only increase its degree of degeneracy regardless the PBH mass. Still, a substantial enhancement of the degree of degeneracy is found for rather low PBH masses, indicating that the degeneracy is of little importance for stellar mass black holes, but may be crucial for low mass black holes. Finally, we address the exotic situation in which a PBH replaces the atomic nucleus of an ordinary atom. In fact, for rather low mass PBHs the electronic ground state turns out to be of the same order as the ordinary Bohr radius.


 
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